Add display of eventual result RowDescription (if any) to the output

of Describe on a prepared statement.  This was in the original 3.0
protocol proposal, but I took it out for reasons that seemed good at
the time.  Put it back per yesterday's pghackers discussion.

src/backend/commands/prepare.c

@@ -10,7 +10,7 @@
  * Copyright (c) 2002-2003, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/prepare.c,v 1.16 2003/05/06 20:26:26 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/prepare.c,v 1.17 2003/05/06 21:51:41 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -393,6 +393,34 @@ FetchPreparedStatementParams(const char *stmt_name)
 	return entry->argtype_list;
 }
 
+/*
+ * Given a prepared statement, determine the result tupledesc it will
+ * produce.  Returns NULL if the execution will not return tuples.
+ *
+ * Note: the result is created or copied into current memory context.
+ */
+TupleDesc
+FetchPreparedStatementResultDesc(PreparedStatement *stmt)
+{
+	Query  *query;
+
+	switch (ChoosePortalStrategy(stmt->query_list))
+	{
+		case PORTAL_ONE_SELECT:
+			query = (Query *) lfirst(stmt->query_list);
+			return ExecCleanTypeFromTL(query->targetList, false);
+
+		case PORTAL_UTIL_SELECT:
+			query = (Query *) lfirst(stmt->query_list);
+			return UtilityTupleDescriptor(query->utilityStmt);
+
+		case PORTAL_MULTI_QUERY:
+			/* will not return tuples */
+			break;
+	}
+	return NULL;
+}
+
 /*
  * Implements the 'DEALLOCATE' utility statement: deletes the
  * specified plan from storage.